1. Field of the Invention
The present invention relates to a camera having an auto focus apparatus.
2. Related Background Art
In a conventional technique for photographing a plurality of objects at different positions in an in-focus state, a camera is set in a stopped-down-aperture aperture state and an f-number or an aperture value is determined so as to obtain a depth of field which covers all the objects.
Under these circumstances, photographing precision greatly depends on the user's experiences. Such a technique is not suitable for an unskilled user, and the resultant picture is often out of focus.
U.S. Pat. No. 4,219,261 describes an auto focus camera. In this camera, data representing setting positions of a photographing lens for objects in different positions are stored in a memory, a sum of the setting positions is obtained, and a middle one of the setting positions is calculated from the sum signal. The photographing lens is manually moved to the middle position, and at the same time the corresponding aperture value (AV) is calculated according to differences between the setting positions so that the objects in the different positions can be simultaneously set in the in-focus state.
In the above camera, however, since the middle position and the aperture value are calculated according to the actual setting positions of the lens for the objects in different positions, focusing precision is degraded. In addition, even if the aperture is controlled according to the above-mentioned aperture value, it is difficult to set all the objects in the different positions in an in-focus state. More specifically, even if the lens is set in the middle position between two lens setting positions, a lens displacement to one lens setting position does not always coincide with that to the other lens setting position. Therefore, the aperture value derived from the two lens setting positions does not coincide with an aperture value represented by the depth of field which covers the above-mentioned lens displacements. Then, this camera cannot satisfactorily obtain a depth of field which covers both objects, thus resulting in an out-of-focus condition. Furthermore, since the lens is manually displaced in this camera, manual focusing operation for the two objects and therefore manual displacement of the lens to the middle position are required and high-speed photographing cannot be performed.